1. Field of the Invention
This invention relates to a variable bandwidth control system and, in particular, to a method of controlling access to a communications link by traffic types that require different fractions of transmission facilities simultaneously. Accordingly, it is a general object of this invention to provide new and improved systems and methods of such character.
2. General Background
Some available software releases used in telecommunications utilize a First In First Out (FIFO) scheme in which traffic requests are served in the order in which they arrive, regardless of the transmission capacity that each request utilizes. Disadvantageously, minimal or no effort is made to separate traffic types by the required amount of bandwidth.
Two other schemes, proposed (in a different context) in an article by B. Kraimeche and M. Schwartz, IEEE J. Select. Areas in Comm., vol SAC 4, September 1986, include:
M1--allows wider band traffic to preempt narrowband requests.
M2--wider band traffic is given priority over narrowband, but preemption is not allowed.
The foregoing prior systems lack certain desirable features. For example, FIFO causes inefficient use of the transmission facility because narrowband traffic requests that arrive between wideband traffic requests cannot be initially grouped and then served. Thus, the transmission facility is utilized with less than 100% effectiveness even when there are pending serviceable traffic requests.
T1 networks are private line networks using T1-carrier (1.544 Mbs digital transmission facilities) and reconfigured ("slow switched") using Digital Cross-Connect Systems (DCS). However, M1 is not practical for T1 networks as it carries business services that cannot be preempted, once begun and subsequently served.
M2 allows for small increases in wideband traffic to have a disproportionate impact on narrowband traffic, although the wideband traffic may be sufficiently important to a network provider to deserve a higher grade of service. M2 cannot be adjusted to accommodate such a requirement.
The foregoing systems, FIFO, M1 and M2, are fixed control policies, and cannot be graduated to reflect the changing importance of traffic offered to a transmission facility.